In general, blood withdrawal devices are used to draw blood samples for analytical purposes and particularly are used by diabetics who must regularly monitor their blood glucose levels. Lancet devices are commonly used to prick the skin so that a few drops of blood may be extracted for testing. The lancet, which typically has a needle fixed to a holder, forces the needle out of the device so that the needle can penetrate the skin.
An example is described in U.S. Pat. No. 4,517,978 in which a lancet has a needle that is attached to and is engaged with a main body. By pressing the trigger of the invention of the abovementioned patent document, the sleeve of the main body is pulled and then the lancet moves forward so that the needle can penetrate the skin for withdrawal of blood. Immediately thereafter the lancet is retracted.
In general, a needle held in a lancet is moved at a high speed in order to withdraw blood by producing a wound in a body part that causes a pain associated with the production of the puncture wounds necessary for the withdrawal of blood, which is problematic. Hence it is desirable to develop a painless blood withdrawal device, especially for those who draw blood samples for analytical purposes and for diabetics who frequently withdraw blood by themselves.
In cases where several patients are tested consecutively such as in hospitals, there is often a risk of a spread of infection by the use of a single lancet device on more than one patient. In order to counteract such problems, the use of a disposable lancet became mandatory. Therefore disposable lancets should be used in hospitals where several patients are tested consecutively. Hence it is also desirable to develop a painless blood withdrawal device with a disposable lancet.
Already several attempts have been made in the prior art to reduce pain associated with the lancing by reducing the thickness of the tip of the needles. However there is a technical limitation for reducing the thickness of the tip of the needles since the needle protective cap is designed to be removed from the main body by human hand.